The metabolic support of lactation is important because increasing numbers of women are electing to breastfeed. More must be known about the associated benefits and risks. Proper support of lactation includes maintaining maternal health. Storage and utilization of body fat supports lactation and maintains metabolic health of the mother. The hypotheses are that 1) the beta- adrenergic receptors as well as the intracellular cascade of adenyl cyclase, protein kinase and hormone sensitive lipase and 2) the activity of the sympathetic nervous system partially regulate adipose tissue metabolism in support of lactation. These hypotheses will be tested by estimating numbers of s-adrenergic receptors and activity of these enzymes during pregnancy and lactation. A subsequent hypothesis is that the receptors and the enzymes are regulated by those hormones which also stimulate mammary growth and lactogenesis. Therefore, the effects and interactions of estrogen, progesterone, growth hormone, and prolactin, as well as corticosteroids and insulin, on these systems Will be determined in in vitro adipose explant culture. A premise herein is that domestic animals, especially swine, are better models for human metabolism than the rat. Therefore, in addition to rat studies, adipose tissue biopsies will be taken from pregnant and lactating swine and bovine to determine adaptations and regulation as listed above. Two lines of bovines genetically selected for milk production will be used to identify those adipose processes most closely associated with lactation. The adaptations in the sympathetic nervous and the adrenal systems will be determined by measuring adipose tissue norepinephrine and epinephrine content; and by glyoxylate staining for catecholaminergic nerve endings. Catecholamine turnover studies will be conducted if results indicate such an involvement. Body fat content, energy intake, milk energy secretion and energy balance will be used to identify the quantitative contribution of each to adipose adaptations. These studies will help define the quantitative adipose tissue support of lactation, determine appropriateness of experimental models and will help define biological mechanisms which allow maximum milk production while ensuring maternal health. Because we will generate quantitative data on body fat metabolism during lactation of growing animals, these studies can eventually assist health care professionals to monitor and support the health status of lactating mothers.